1. Field of the Invention
This invention relates to a process of vapor phase catalytic hydrogenation of maleic anhydride to gamma-butyrolactone (BLO) and tetrahydrofuran (THF), and, more particularly, to a multistage process in which the crude reactor effluent from the first stage hydrogenation is partially hydrogenated to tetrahydrofuran in a second stage hydrogenation to form a product mixture of gamma-butyrolactone and tetrahydrofuran in a selected ratio.
2. Description of the Prior Art
A continuous process is known for the manufacture of tetrahydrofuran by catalytic hydrogenation of maleic anhydride (MA) and/or succinic anhydride (SA) with the formation of gamma-butyrolactone (GBL) as an intermediate, in accordance with the following equations: ##STR1##
However, different mixtures, depending on the hydrogenation catalyst used, of intermediate products and end products, e.g. succinic acid, butyrolactone, tetrahydrofuran and butanediol, as well as propanol and butanol, and polymeric esters of the above compounds, are formed.
Various hydrogenation catalysts have been disclosed for carrying out such a hydrogenation process. See, for example, U.S. Pat. Nos. 3,065,243; 3,580,930; 3,829,448; 3,894,054; 3,853,922; 4,001,282; 4,105,674; 4,083,809; 4,006,165; 4,810,807; and EPA 332,140.
U.S. Pat. No. 4,048,196, for example, described a multistage process for the manufacture of butanediol and/or tetrahydrofuran from maleic anhydride or succinic anhydride via gamma-butyrolactone intermediate. In this process, (a) maleic anhydride or succinic anhydride was hydrogenated in the presence of gamma-butyrolactone over a fixed-bed catalyst containing nickel to give gamma-butyrolactone; then (b) the water formed during the hydrogenation was removed by feeding the reaction mixture to the middle section of a distillation column; then isolating water and gamma-butyrolactone, on one hand, and succinic anhydride and gamma-butyrolactone on the other; recycling the succinic anhydride and gamma-butyrolactone; and separating the gamma-butyrolactone and water by distillation; and (c) hydrogenating gamma-butyrolactone over a catalyst containing copper into butanediol and/or tetrahydrofuran. However, in this process, it was necessary to obtain the gamma-butyrolactone as the sole product of the hydrogenation of maleic anhydride, and, in a separate, off-line stage, to convert the isolated butyrolactone into butanediol and tetrahydrofuran.
Accordingly, it is an object of this invention to provide a process of vapor phase hydrogenation of maleic anhydride to a predetermined mixture of gamma-butyrolactone and tetrahydrofuran by multistage hydrogenation without separating any by-products or isolating the gamma-butyrolactone intermediate.